myProcess.StartInfo.UseShellExecute = false;
                myProcess.StartInfo.FileName = txt_ClientPath.Text;
                myProcess.StartInfo.CreateNoWindow = true;
                myProcess.Start();

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Text;

namespace Text
{
    public class Program
    {
        [DllImport("user32.dll")]
        static extern IntPtr GetTopWindow(IntPtr hWnd);

        [DllImport("user32.dll")]
        static extern Int32 GetWindowText(IntPtr hWnd, StringBuilder lpString, int nMaxCount);

        [DllImport("user32.dll")]
        static extern int GetClassName(IntPtr hWnd, StringBuilder lpClassName, int nMaxCount);

        [DllImport("user32.dll")]
        static extern IntPtr GetWindow(IntPtr hWnd, UInt32 uCmd);

        [DllImport("user32.dll")]
        static extern uint GetWindowThreadProcessId(IntPtr hWnd, out uint lpdwProcessId);

        private static readonly UInt32 GW_HWNDNEXT = 2;

        static Int32 Run()
        {
            Process myProcess = new Process();
            myProcess.StartInfo.UseShellExecute = false;
            myProcess.StartInfo.FileName = "notepad.exe";
            myProcess.StartInfo.CreateNoWindow = true;
            myProcess.Start();
            myProcess.WaitForExit(2000);

            return myProcess.Id;
        }

        static IntPtr GetWnd(Int32 pID,String className, String text)
        {
            IntPtr h = GetTopWindow(IntPtr.Zero);
            while (h != IntPtr.Zero)
            {
                UInt32 newID;
                GetWindowThreadProcessId(h, out newID);
                if (newID == pID)
                {
                    StringBuilder sbClassName = new StringBuilder(200);
                    StringBuilder sbText = new StringBuilder(200);

                    GetClassName(h, sbClassName, 200);
                    GetWindowText(h, sbText, 200);
                    if (sbClassName.ToString().IndexOf(className,StringComparison.CurrentCultureIgnoreCase) >= 0 && 
                        sbText.ToString().IndexOf(text,StringComparison.CurrentCultureIgnoreCase) >= 0)
                    {
                        break;
                    }
                }

                h = GetWindow(h, GW_HWNDNEXT);
            }

            return h;
        }

        static void Main(string[] args)
        {
            Console.WriteLine(GetWnd(Run(), "Notepad", "无标题 - 记事本"));

            Console.ReadKey();
        }
    }
}